The present invention relates to a method of forming a minute focusing lens with respect to over an image sensor portion such as a CCD or CMOS.
Conventionally, in an image sensor such as a CCD or CMOS, a minute focusing lens is formed with respect to the respective photoactive area in order to enhancing the focusing efficiency of the photoactive area.
In the above-described minute focusing lens, conventionally, a resin portion formed on the upside of the focusing portion is formed into a lens configuration by heat melting.
An example of this method will now be briefly explained below with reference to FIG. 4.
Incidentally, in FIG. 4, a reference numeral 301 denotes a device substrate (image sensor substrate), 302 denotes a silicon wafer, 303 denotes a photoactive area, 304 denotes a color filter, 304a denotes a flattening layer, 305 denotes a flattening layer, 306 denotes a resist layer, 307 denotes a photo-mask, 308 denotes exposure light, 309 denotes a resist pattern (post-development resist image), and 310 denotes a convex lens (post-heat-melting resist image).
This example is a case where, with respect to the device substrate 301 (FIG. 4A) having the color filter 304 disposed on the upside of the photoactive area 303 formed in one surface of the silicon wafer 302, a minute focusing lens is provided correspondingly to that photoactive area 303.
First, the flattening layer 305 covering the color filter 304 of the device substrate 301 is provided and, further, on this flattening layer 305, there is coated the resist layer 306 which is a photo-sensitive resin for forming the lens. (FIG. 4B).
Subsequently, in a state where the photo-mask 307 is located near the resist layer 306, the resist layer 306 is selectively exposed to light (FIG. 4C), and is development-treated to form in the region corresponding to the respective photoactive area 303 the resist pattern 309 that covers the photoactive area 303 and that is substantially shaped like a square. (FIG. 4D).
Thereafter, heat treatment is performed to cause the resist pattern 309 to heat melting to form the convex lens 310 corresponding to the respective photoactive area 303. (FIG. 4E).
In the case of this method, because forming the resist pattern 309 into the convex configuration by heat melting, it had the difficulty of forming a lens of good focusing efficiency having a desired focal distance.
Especially, in the CMOS image sensor having a significantly great distance up to the photoactive area, as far as concerning natural melting caused by heat treatment, it is impossible to form a lens configuration that is made as designed and that has a long focal distance.
As described above, conventionally, in the method of forming a minute focusing lens with respect to over the image sensor portion such as a CCD or CMOS, the lens configuration is formed by heat melting. Therefore, it is difficult to obtain a desired configuration, and, in addition, a limitation is also imposed upon the focusing efficiency. And, there has been a demand for appearance of the measure for coping with such circumstance.
The present invention has been made in order to cope with that circumstance and has an object to provide a method which, in a method of forming a minute focusing lens with respect to over the image sensor portion such as a CCD or CMOS, enables forming a lens of designed configuration having a good focusing efficiency.
To attain the above object, according to one aspect of the present invention, there is provided a method of forming a minute focusing lens being arranged to form a minute focusing lens with respect to over a photoactive area of an image sensor such as a CCD or CMOS, comprising; coating a resist film on a flattening layer formed over the photoactive area of the image sensor; exposing the resist film to light via a photo-mask; developing the resist film; and patterning the resist film into a lens configuration, wherein the photo-mask is a light transmission type having no light-shading layer and the photo-mask has provided thereon a light transmission portion comprising a light refraction material, having on its surface portion stairs portion, the stairs portion having the phase of a transmission light at its respective position controlled relative to a prescribed width so that a desired light intensity distribution may be obtained at the surface of the photo-mask light-exposed portion.
Further, the photo-mask, according to the phase shifting data, determined by calculation from the light intensity distribution data on the surface of the light-exposed portion matching with the configuration of the focusing lens desired to be formed and having obtained therefrom such light intensity distribution, of the transmission light at the respective position of the photo-mask, has the thickness at its respective position determined relative to a prescribed width of the phase shifting of the transmission light, to thereby provide a binary grating to the photo-mask configuration, and the photo-mask structure is worked into a configuration matching with that binary grating, whereby the photo-mask is the one having formed thereon the light transmission portion comprising a light refraction material, having on its surface the stairs portion.
Further, this method is the one which, in the above-described method, comprises, after patterning, radiating far ultra-violet rays and thereby curing the resin and bleaching the photo-sensitive material.
Incidentally, here, the wording xe2x80x9cthe respective position of the photo-maskxe2x80x9d means the two-dimensional position that can be regarded as being two-dimensional position in the plane direction of the photo-mask, and the phase shifting of the transmission light at the respective position of the photo-mask, of course, corresponds to the change in thickness at the respective position of the photo-mask.
Further, as the method of forming the above-described mask having the stairs portion, there can be taken up, for example, a technique of performing multi-stage etching of the mask substrate, or a method of forming by performing deposition, etc. onto the mask substrate.
The method of forming a minute focusing lens according to the present invention is provided, by its being made up into the above-described construction, as a method which, in the method of forming a minute focusing lens over the image sensor portion such as a CCD or CMOS, enables forming a lens of designed configuration having a good focusing efficiency.
Specifically, the present method is realized by the one which comprises coating a resist film on a flattening layer formed over the photoactive area of the image sensor, exposing the resist film to light via a photo-mask, developing the resist film, and patterning the resist film into a lens configuration, whereby the photo-mask is a light transmission type having no light-shading layer and the photo-mask is the one having provided thereon a light transmission portion comprising light refraction material, having on its surface portion a stairs portion, the stairs portion having the phase of a transmission light at its respective position controlled relative to a prescribed width so that a desired light intensity distribution may be obtained at the surface of the photo-mask light-exposed portion.
For the photo-mask, there can be taken up, as the one that is at a practical-use level viewed from the aspect of manufacture, the photo-mask which, according to the phase shifting data, determined by calculation from the light intensity distribution data on the surface of the light-exposed portion matching with the configuration of the focusing lens desired to be formed and having obtained therefrom such light intensity distribution, of the transmission light at the respective position of the photo-mask, has the thickness at its respective position determined relative to a prescribed width of the phase shifting of the transmission light, to thereby provide a binary grating to the photo-mask configuration, and the photo-mask structure being worked into a configuration matching with that binary grating, whereby the photo-mask is the one having formed thereon the light transmission portion comprising a light refraction material, having on its surface the stairs portion.
Further, by, after patterning, further radiating far ultra-violet rays and thereby curing the resin and bleaching the photo-sensitive material, it is possible to enhance the transmission characteristic of the development-formed focusing lens.
The present invention, as described above, has enabled providing a method of, in the method of forming a minute focusing lens with respect to over the image sensor portion such as a CCD or CMOS, forming a lens having a designed configuration that provides a good light focusing efficiency.